Chevrolet Silverado / GMC Sierra. Manual — part 812
information is used for engine controls as well as determining the transmission shift patterns. The
state of each input is available for display on the scan tool. The five input parameters represented
are Signal A, Signal B, Signal C, Signal P (Parity) and Signal N (P/N Start).
INPUT SPEED SENSOR (ISS)
Fig. 202: Identifying Input Speed Sensor (ISS)
Courtesy of GENERAL MOTORS CORP.
The input speed sensor (ISS) is a hall-effect type sensor. The ISS mounts to the control valve
upper body assembly and connects to the control solenoid (w/body and TCM) valve assembly
through a wire harness and connector. The sensor faces the 1-2-3-4 and 3-5-R clutch housing
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,
Sierra & Silverado
machined teeth surface. The sensor receives 8.3-9.3 volts on the ISS/OSS Supply Voltage circuit
from the TCM. As the 1-2-3-4 and 3-5-R clutch housing rotates, the sensor produces a signal
frequency based on the machined surface of the 1-2-3-4 and 3-5-R clutch housing. This signal is
transmitted through the ISS signal circuit to the control solenoid (w/body and TCM) valve
assembly. The control solenoid (w/body and TCM) valve assembly uses the ISS signal to
determine line pressure, transmission shift patterns, torque converter clutch (TCC) slip speed and
gear ratio.
OUTPUT SPEED SENSOR (OSS)
Fig. 203: Identifying Output Speed Sensor (OSS)
Courtesy of GENERAL MOTORS CORP.
The output speed sensor (OSS) is a hall-effect type sensor. The OSS mounts to the control valve
upper body assembly and connects to the control solenoid (w/body and TCM) valve assembly
through a wire harness and connector. The sensor faces the output shaft machined teeth surface.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,
Sierra & Silverado
The sensor receives 8.3-9.3 volts on the ISS/OSS supply voltage circuit from the TCM. As the
output shaft rotates, the sensor produces a signal frequency based on the machined surface of the
output shaft. This signal is transmitted through the OSS signal circuit to the TCM. The TCM uses
the OSS signal to determine line pressure, transmission shift patterns, torque converter clutch
(TCC) slip speed and gear ratio.
AUTOMATIC TRANSMISSION INLINE 16-WAY CONNECTOR DESCRIPTION
Fig. 204: Identifying Automatic Transmission Inline 16-Way Connector
Courtesy of GENERAL MOTORS CORP.
The transmission electrical connector is an important part of the transmission operating system.
Any interference with the electrical connection can cause the transmission to set diagnostic
trouble codes or affect proper operation. The following items can affect the electrical connection:
Bent pins in the connector from rough handling during connection and disconnection
Wires backing away from the pins or coming uncrimped, in the external wiring harness
Dirt contamination entering the connector when disconnected
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,
Sierra & Silverado
Transmission fluid leaking into the connector, wicking up into the external wiring harness
and degrading the wire insulation
Moisture intrusion in the connector
Low pin retention in the external connector from excessive connection and disconnection of
the wiring connector assembly
Pin corrosion from contamination
Damaged connector assembly
Remember the following points:
Limit twisting or wiggling the connector during removal. Bent pins can occur.
Do not pry the connector off with a screwdriver or other tool.
Whenever the transmission external wiring connector is disconnected from the internal
harness and the engine is operating, DTCs will set. Clear these DTCs after reconnecting the
external connector.
Use the following procedure to disconnect the engine side of the 16-way connector from the
transmission side:
1. Unlock the slide lock on the engine wiring harness connector.
2. Rotate the connector lever counterclockwise and remove the connector from the electrical
connector passage sleeve.
Use the following procedure to reconnect the engine side of the 16-way connector to the
transmission side:
1. Orient the alignment slot on the engine side of the connector with the alignment tab on the
electrical connector passage sleeve.
2. Slide the engine side connector through the electrical connector passage sleeve and into the
transmission side connector.
3. Rotate the connector lever clockwise until the connector is fully seated.
4. Lock the slide lock on the connector.
PARK - ENGINE RUNNING
When the gear selector lever is in the Park (P) position, fluid is drawn into the pump through the
transmission fluid filter assembly, from the transmission fluid pan assembly. Line pressure is then
directed to the following valves:
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,
Sierra & Silverado
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